Method for heat and humidity exchange between two air streams and apparatus therefor

ABSTRACT

An apparatus and method for heat and humidity exchange between two air streams, one hot and one humid. A first of the air streams is fed from the interior of a building to the ambient air and a second of the air streams is fed from the ambient air to the interior of the building. The first air stream is cooled and transferred through a heat exchanger, to a heater and a dehumidifier before being exhausted to the ambient air. The second air stream is transferred through the dehumidifier and the heat exchanger, whereupon it is cooled in a cooling device before being transferred into the interior to the building. Before being fed to the dehumidifier, the second air stream is caused to exchange heat and humidity with the first air stream before the latter is fed into the heat exchanger.

BACKGROUND OF THE INVENTION

The invention relates to a method for heat and humidity exchange betweentwo air streams, one of which being hot and humid, at least during afirst part of the year, wherein a first of said air streams is fed fromthe interior of a building to the ambient air and a second of said airstreams is fed from said ambient air to the interior of said building,whereby said first air stream is cooled and thereafter transferredthrough a heat exchanger, whereupon it is transferred to a heater andthereafter transferred through a dehumidifier before being exhausted tothe ambient air, whereas said second air stream is transferred throughsaid dehumidifier and thereafter through said heat exchanger, whereuponit is cooled in a cooling device before being transferred into theinterior of said building.

The invention relates also to an apparatus for heat and humidityexchange between two air streams, one of which being hot and humid, atleast during a first part of the year, wherein a first of said airstreams is adapted to be fed from the interior of a building to theambient air and a second of said air streams is adapted to be fed fromsaid ambient air to the interior of said building, said apparatuscomprises a housing, divided into first and second compartments, meansfor transportation of the two air streams separately in saidcompartments, a device for cooling and humidification of the first airstream, a sensible heat exchanger for exchange of heat between the twoair streams, a heater for heating said first air stream, and adehumidifier for drying said second air stream, wherein said first airstream is adapted to be transferred through said dehumidifier forregenerating said dehumidifier.

Apparatuses and methods for heat and humidity exchange between two airstreams are known. Such apparatuses and methods are used for improvingthe indoor air in, for instance, small houses and buildings, i.e. tocool and to dry the outdoor air which is fed into a building during thesummer and to heat and humidify said air during the winter before saidair is transferred into the building.

However, there is a problem when the outdoor air is hot and humid, i.e.when the temperature is above 35° C., and the content of water in theoutdoor air is larger than 11 g/kg air, since the known apparatuses cannot treat such air in the proper way.

Also, there is a problem with the energy consumption, which is oftenquite high. The energy is used to either regenerate a dehumidifierduring the summer or to heat the supply air during the winter. Moreover,the production of energy may result in air pollution, and especially inundesired outlet of CO₂.

Therefore, it would be desirable to provide a method and an apparatus bywhich it is possible to save energy.

SUMMARY OF INVENTION

The object of the present invention is to eliminate the above-mentioneddrawbacks and to provide a method and an apparatus which will operateunder the above conditions and by which it is also possible to minimizethe energy consumption.

According to a first aspect of the invention this object is achieved inthat said second air stream, before being fed to said dehumidifier, iscaused to exchange heat and humidity with said first air stream beforethe latter is fed into said heat exchanger.

According to a second aspect of the invention this object is achieved inthat an enthalpy exchange device is provided in said housing and adaptedto treat said second air stream and said first air stream for exchangeof heat and humidity between said air streams, before said second airstream is transferred through said dehumidifier and said first airstream is transferred through said humidifier, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting example of the invention will now be described withreference to the drawings, in which FIG. 1 is a perspective view of anapparatus according to the invention comprising a lower housing unit andan upper housing unit, shown separated from each other, FIG. 2 is a viewfrom above of the lower housing unit of the apparatus according to theinvention and FIG. 3 is a view from above of the upper housing unit ofthe apparatus according to the invention.

To be able to better understand the method according to the invention anapparatus for carrying out said method will be described first.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an apparatus according to the invention for heat andhumidity exchange between two air streams, wherein a first of said airstreams is fed from the interior of a building to the ambient air and asecond of said air streams is fed from said ambient air to the interiorof said building.

As seen in FIGS. 1-3, in a preferred embodiment of the invention, theapparatus comprises a housing 1,2 divided into a lower housing unit 1and an upper housing unit 2. Each of said housing units are also dividedinto first and second compartments, respectively, for transferring thetwo air streams separately in said housing units.

In a first mode of operation, the summer mode, the first air stream,exhaust air, which is represented by a continuous arrow in FIGS. 1-3, isfed into an inlet 3 of the first compartment, which inlet 3 is arrangedin a first end of the lower housing unit 1, by a fan 11. The first airstream is then transferred through a filter 12, and then through anenthalpy exchange device 13, in which the two air streams exchange heatand moisture with each other. From said enthalpy exchange device 13 thefirst air stream is fed through a device 14 for evaporative cooling,direct or indirect, or indirect cooling, using water other coolant orrefrigerant, and humidification in which said first air stream is cooledand humidified, and therefrom to the first compartment of the upperhousing unit 2. In said first compartment the exhaust air is fed througha sensible heat exchanger 21 of cross flow or rotary type for exchangeof heat only with the second air stream, then through a heater 22 andfinally through a dehumidifier 23. The first air stream or only aportion of said first air stream, heated in said heater 22, is used toregenerate the dehumidifier 23, which preferably is a desiccantdehumidifier of rotor type. Said first air stream is then exhaustedthrough an outlet 5 in the first compartment into the ambient air.

The second air stream, outdoor air, which is represented by a dashedarrow in FIGS. 1-3, is fed into an inlet (not shown) of the secondcompartment, which inlet is arranged in the second end of the lowerhousing unit 1, by a fan 24 (see FIG. 3). The second air stream is thentransported through a filter 15 and from said filter 15 through theabove-mentioned enthalpy exchanger device 13. Thereafter said second airstream is transferred to the second compartment of the upper housingunit 2 and through the dehumidifier 23, then through the heat exchanger21 and finally through an additional heater 25 and an additionalhumidifier 26, respectively, before being exhausted through an outlet 6in the second compartment into the building. Said heater 25 and saidhumidifier 26 is non-operable in summer mode of operation. Saidhumidifier 26 may be used as a second stage of cooling in this mode. Inthis case the humidifier 26 is replaced by a cooling device with nohumidification properties.

The function of the sensible heat exchanger 21 is to exchange heat andno or very little humidity between the two air streams.

In the second mode of operation, the winter mode, the function of thesensible heat exchanger, the device 14 for cooling and humidificationand the heater 22 and the rotation of the desiccant rotor 23 isdisabled, and if the sensible heat exchanger is a cross flow heatexchanger 21 the first air stream is bypassed said heat exchangerthrough a duct 27 which can be closed by a damper (not shown) allowingthe system to act as a heater and humidity recovery device utilizing theenthalpy rotor 13 only for this purpose.

However, if the temperature of the first air stream under theseconditions is below about +3° C. after it has passed the heat exchanger21 a certain amount of said air stream is transferred through the heatexchanger 21 to avoid that ice is formed on the heater 22, since saidheater is not used in this mode of operation. Heater 25 and humidifier26 are used in this mode of operation to heat and humidify the first airstream to comfort indoor conditions.

The two heaters 22,25 of the apparatus according to the invention usepreferably district heating to heat first and second air streams,respectively. However, it is obvious for the man skilled in the art thatother types of energy, in particular low cost forms, such as natural gasor solar heated water, or other waste heat sources, could be used forheating said heaters.

In different embodiments of the invention the enthalpy exchange device13 could be an enthalpy wheel or a cross flow enthalpy exchanger block.Likewise, the device 14 could be a evaporative cooler or other type ofcooling device using indirect cooling in which water, other coolingagent or refrigerant is used, and the heat exchanger 21 could be asensible exchange wheel or a cross flow plate-type heat exchanger.Moreover, the humidifier 26 can in the summer mode of operation bereplaced by a cooling device with no humidification properties and inthe winter mode of operation by a humidifier with more or less nocooling properties.

Moreover, the dehumidifier 23 is preferably a desiccant rotor, but canbe of any other type of dehumidifier.

In another embodiment of the invention the humidifier 14 and thesensible heat exchanger 21 could be replaced by a single dew pointexchange device, i.e. an indirect evaporative cooler, which is used tocool the supply air.

In different embodiments of the invention the above-mentioned enthalpyexchange device, dehumidifier and heat exchanger are provided with meansof capacity control, as is known by the artisan.

Moreover, in embodiments utilizing cross-flow rather than rotary heatexchanger or enthalpy exchange devices dampers (not shown) may bearranged to bypass air around these devices or groups of devices ofwhich the exchangers are included as means of capacity control.

The advantage of the apparatus according to the invention is that it hasvery low energy consumption compared to known apparatus, that itprovides individual control over humidity and cooling requirements andthat it will work at higher ambient specific humidities than priordesiccant cooling type devices.

The method according to the invention will now be described first inconnection the summer mode of operation.

The first air stream, exhaust air, is fed first, seen in the directionof flow of said air stream, through the inlet 3 of the first compartmentof the lower housing unit 1 by the fan 11, whereupon it is transferredthrough the filter 12 and the enthalpy exchange device 13. Then saidfirst air stream is transferred through the device 14 for cooling andhumidification from which it is fed to the first compartment of theupper housing unit 2. In said upper housing unit 2 it is transferredthrough the cross flow heat exchanger 21, the heater 22 and thedehumidifier 23, where-upon it is exhausted through the outlet 5 intothe ambient air.

The second air stream, outdoor air, is fed first, seen in the directionof flow of said air stream, through the inlet (not shown) of the secondcompartment of the lower housing unit 1 by the fan 24 and then throughthe filter 15 and the enthalpy exchange device 13. Therefrom said secondair stream is transferred to the second compartment of the upper housingunit 2. In said upper housing unit 2 the second air stream istransferred through the dehumidifier 23, the cross flow heat exchanger21, the additional heater 25 and the additional humidifier 26, whereuponit is exhausted through the outlet 6 into the building.

In the second mode of operation, the winter mode, the first air stream,exhaust air, is fed in the same way as in the first mode of operationexcept that said air stream does no pass through the heat exchanger 21or a small amount is passed through said heat exchanger in the case thetemperature of the said stream is below about +3° C. when the air streamreaches the heater 22 to avoid formation of ice on said heater, since itis not used in this mode of operation. The second air stream istransferred through the lower and upper housing units 1,2 in the sameway as in the first mode of operation.

What is claimed is:
 1. A method for heat and humidity exchange betweentwo air streams, one of which being hot and humid, at least during afirst part of the year, wherein a first of said air streams is fed fromthe interior of a building to the ambient air and a second of said airstreams is fed from said ambient air to the interior of said building,whereby said first air stream is cooled and thereafter transferredthrough a heat exchanger, whereupon it is transferred to a heater andthereafter transferred through a dehumidifier before being exhausted tothe ambient air, whereas said second air stream is transferred throughsaid dehumidifier and thereafter through said heat exchanger, whereuponit is cooled in a cooling device before being transferred into theinterior of said building, characterized in that said second air stream,before being fed to said dehumidifier, is caused to exchange heat andhumidity with said first air stream before the latter is cooled. 2.Method according to claim 1, wherein said second air stream is, at leastduring a second part of the year, cooler and less humid in absoluteterms than said first air stream, characterized in that said first airstream only is brought to exchange heat and humidity with said secondair stream.
 3. Method according to claim 2, characterized in that saidsecond air stream is transferred through an additional heater afterbeing transferred through said heat and humidity exchanger.
 4. Methodaccording to claim 3, characterized in that said second air stream istransferred through an additional humidifier before or after beingtransferred through said additional heater.
 5. An apparatus for heat andhumidity exchange between two air streams, one of which being hot andhumid, at least during a first part of the year, and in which a first ofsaid air streams is adapted to be fed from the interior of a building tothe ambient air and a second of said air streams is adapted to be fedfrom said ambient air to the interior of said building, said apparatuscomprises a housing (1, 2), divided into first and second compartments,means (11, 24) for transportation of the two air streams separately insaid compartments, a device (14) for cooling and humidification of thefirst air stream, a sensible heat exchanger (21) for exchange of heatbetween the two air streams, a heater (22) for heating said first airstream, and a dehumidifier (23) for drying said second air stream,wherein said first air stream is adapted to be transferred through saiddehumidifier (23) for regenerating said dehumidifier, characterized inthat an enthalpy exchange device (13) is provided in said housing (1, 2)and adapted to treat said second air stream and said first air streamfor exchange of heat and humidity between said air streams before saidsecond air stream is transferred through said dehumidifier (23) and saidfirst air stream is transferred through said device (14) for cooling andhumidification, respectively.
 6. Apparatus according to claim 5, whereinsaid second air stream is, at least during a second part of the year,cooler and less humid in absolute terms than the first air stream,characterized in that the heat exchanger (21) and the dehumidifier (23)is deactivated during this second part of the year, either bytermination of the rotation of the heat exchanger or enthalpy exchanger,or by bypass of the air stream around said devices, or if the devicesare stationary block-type devices via a series of dampers.
 7. Apparatusaccording to claim 6, characterized in that an additional heater (25) isprovided in the second compartment after said sensible heat exchanger(21) seen in the flow direction of the second air stream.
 8. Apparatusaccording to claim 6, characterized in that an additional humidifier(26) is provided in the second compartment after said sensible heatexchanger (21) seen in the flow direction of the second air stream,wherein the additional humidifier (26), in the summer mode of operation,is a cooling device with no humidification properties.
 9. Apparatusaccording to claim 5, characterized in that the enthalpy exchange device(13) is an enthalpy wheel.
 10. Apparatus according to claim 5,characterized in that the enthalpy exchange device (13) is a cross flowenthalpy exchanger block.
 11. Apparatus according to claim 5,characterized in that the sensible heat exchanger (21) is a sensibleheat exchange wheel.
 12. Apparatus according to claim 5, characterizedin that the sensible heat exchanger (21) is a cross flow heat exchanger.13. Apparatus according to claim 5, characterized in that a coolingdevice is provided in the second compartment after said heat exchanger(21) seen in the flow direction of the second air stream.
 14. Method ofcontrol of the apparatus according to claim 6, characterized in thathumidity control is accomplished by control of one or more of thefollowing devices, the heater (22), the speed of the desiccantdehumidifier rotor (23), the humidifier (26) or the enthalpy exchanger(21), and that temperature control is achieved by control of one or moreof the following devices, the heater (25), the sensible exchanger (21),humidifier (14), the additional humidifier (26) or the enthalpyexchanger (13).